Method and apparatus for sensing and correcting an overloaded electrical circuit



Nov. 24, 1970 E. F. BEDFORD 3,543,095

METHOD AND APPARATUS FOR SENSING AND CORRECTING AN OVERLOADED ELECTRICAL CIRCUIT Filed Feb. 5. 1968 57 so 48 57 CA4 52 Jul 4s W (3 1, 8 OFF OFF 56 I INVENTOR. EDWARD F. BEDFORD BY i F|G.4 J ,ofl 9izaflallm a 7 7 ATTORNEYS.

United States Patent US. Cl. 317-54 5 Claims ABSTRACT OF THE DISCLOSURE Disclosed is a method and apparatus for sensing and correcting an overloaded electrical circuit including a power supply unit which is defined by an incoming line having a positive and negative side adapted to be connected to a source of electrical power, means to vary the voltage, and output means for connecting electrical apparatus to the power supply unit. The apparatus of this invention is comprised of a circuit breaker connected in series with at least one side of the incoming line and having internal switching means adapted to open in the event of an overloaded condition of the incoming line. The circuit breaker is provided with an external reset arm adapted to reset the internal switching means to a closed position. A key operated tumbler lock including a key plug rotatable in a lock cylinder and a keyway is attached to a panel of the power supply unit such that the keyway is accessible from the exterior of the power supply unit. The key plug of the tumbler lock is interconnected to the external reset arm of the circuit breaker by means of a connecting arm and pin linkage. Thus, the internal switching means of the circuit breaker may be reset by a key inserted in the keyway. The connection between the external reset arm and the internal switching means of the circuit breaker is of the lost motion type permitting the internal switching means to open independently of the external reset arm and the key plug.

The method of this invention comprises the steps of:

(a) Providing a key operated tumbler lock including a key plug rotatable in a lock cylinder with a keyway accessible from the exterior of the power supply unit.

(b) Providing a mechanical linkage between the key plug and an external reset arm of a circuit breaker connected in series with at least one side of an incoming line of the power supply unit; the circuit breaker having internal switching means adapted to open in the event of an overloaded condition of the incoming line and adapted to be reset by the external reset arm.

(0) Providing a lost motion linkage between the internal switching means of the circuit breaker and the key plug permitting the internal switching means to open independently of the key plug in the event of an overloaded condition of the incoming line of the power supply unit.

(d) Connecting electrical apparatus to output means of the power supply unit.

(e) Sensing an open internal switching means condition in the circuit breaker due to an overloaded condition of the incoming line.

(f) Correcting the circuit condition which created the open internal switching means condition.

(g) Inserting a key adapted" to be received in the keyway and turning the key plug to thereby reset the internal switching means of the circuit breaker.

(h) Removing the key from the keyway.

BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for sensing and correcting an overloaded electrical circuit.

More particularly, this invention relates to a method and apparatus for sensing and correcting an electrical circuit assembled by a student in a laboratory. In science laboratories of high schools and colleges, it is customary to conduct experiments involving electrical apparatus wherein the student is permitted to complete an electrical circuit and, after connecting the circuit to a source of electrical power, to observe certain phenomena. Common to practically all experiments involving an electrical circuit is a power supply unit. Power supply units may take several dififerent forms and may include various features and accessories depending upon the end use to which it will be put. However, common to all power supply units will be several basic components including an incoming line adapted to be connected to a source of electrical power, one or more potentiometers adapted to vary the voltage, and an outlet to which may be connected suitable electrical apparatus. While these components are common to nearly all power supply units, additional components such as switches, alternate outlets, output jacks, indicator lights, and meter-s may be provided in the power supply unit to serve a particular function. The power supply unit may also include a circuit breaker adapted to open in the event of an overloaded condition of the circuit assembled by the student. Known prior art power supply units incorporating a circuit breaker, however, include some form of manual reset button or toggle switch means whereby the student can readily reset the circuit breaker to a closed position at his option. It has been found, however, that permitting the student to reset the circuit breaker on his power supply unit may be detrimental to expensive laboratory equipment in that the student may not be capable of determining the source of a short circuit. The result is that continued resetting of the circuit breaker may damage costly electronic eqtipment. In some instances, students have been known to manually hold the circuit breaker closed or bypass the circuit breaker with the result that an overloaded circuit burns out one or more delicate pieces of equipment.

The apparatus and method of this invention provide for sensing and correcting of an overloaded circuit by means of a key operated circuit breaker located within a laboratory power supply unit. Key operation of the circuit breaker permits the instructor to check on student work in the event of a short circuit. With the instructor maintaining possession of the key, the student must call to the attention of the instructor any short circuit condition since the instructor is the only individual capable of resetting the circuit breaker. Thus, the instructor is assured of having an opportunity toinspect the circuit after each occurrence of an overloaded condition.

BRIEF DESCRIPTION OF THE INVENTION Briefly described, this invention relates to a method and apparatus of sensing and correcting an overloaded electrical circuit. The apparatus of this invention is comprised of a key operated tumbler lock including a key plug rotatable in a lock cylinder and a keyway. The tumbler lock is located in a power supply unit comprising an incoming line adapted to be connected to a source of electrical power, potentiometer means to vary the voltage of the power source, and output means for connecting suitable electrical apparatus to the power supply unit. A circuit breaker is mounted within the power supply unit and is connected in series with at least one side of the incoming line. Internal switching means are provided in the circuit breaker adapted to open in the event of an overloaded condition of the incoming line. The circuit breaker further includes an external reset arm adapted to reset the internal switching means to a closed position. Interconnecting linkage means is provided between the key plug of the tumbler lock and the external reset arm whereby the internal switching means of the circuit breaker may be reset by a key inserted in the keyway of the tumbler lock. In order to permit the internal switching means of the circuit breaker to open independently of the key plug, lost motion means is provided between the internal switching means and the key plug.

Briefly described the method of this invention comprises the steps of:

(a) Providing a key operated tumbler lock including a key plug rotatable in a lock cylinder. The tumbler lock is mounted on a power supply unit including an incoming line adapted to be connected to a source of electrical power, potentiometer means to vary the voltage, and output means'for connecting electrical apparatus. The tumbler lock is mounted on the power supply unit such that the lock keyway is accessible from the exterior of the unit.

(b) Providing a mechanical linkage between the key plug of the tumbler lock and an external reset arm of a circuit breaker connected in series with at least one side of the incoming line and including internal switching means adapted to open in the event of an overloaded condition of the incoming line.

Providing a lost motion linkage between the internal switching means of the circuit breaker and the key plug permitting the internal switching means to open independently of the key plug.

((1) Connecting electrical apparatus to the power supply unit output means.

(e) Sensing an open internal switching means condition in the circuit breaker.

(f) Correcting the circuit condition which created the open internal switching means condition.

(g) Inserting a key adapted to be received in the keyway and turning the key plug to reset the internal switching means.

(h) Removing the key from the keyway.

DESCRIPTION OF THE INVENTION A more complete description of the method and apparatus of this invention will now be made with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a laboratory power supply unit and showing the tumbler lock, an element of the apparatus of this invention, mounted thereon,

FIG. 2 is an end elevation view of the circuit breaker and tumbler lock of this invention,

FIG. 3 is a top view, partly in section, of the circuit breaker and tumbler lock as mounted to the face of a power supply unit and showing the circuit breaker in the closed or on position,

FIG. 4 is a top view similar to FIG. 3 and showing the circuit breaker in an open or off position,

FIG. 5 is a view taken along the line 5-5 of FIG. 3.

Referring more particularly to FIG. 1, there is shown a laboratory power supply unit 10 including a case 12 and a front panel 14. Panel 14 may be secured to case 12 by means of fasteners 16 or other connecting means well known to those skilled in the art. A pair of front panel handles 18 vare provided for ease of installation of the power supply unit. Mounted on the face of panel 14 are a plurality of control knobs 20, 22 and 24, outlets 26, 28, output jacks 30, 32 and 34 and an indicator light 36. Basically, the control knobs 20-24 function to vary the output of the power supply at the output jacks 30-34. One or more potentiometers are located within the case 12 of the power supply unit and are controlled by the knobs 20-24. The indicator light 36 serves to visually indicate that the power supply unit is supplying power at the outlet jacks.

The power supply unit as shown in FIG. 1 illustrates a typical laboratory unit to which the apparatus and method of this invention may be applied. The power supply unit as shown in FIG. 1 should not be considered as limiting to this invention as many combinations of switches, outlets, potentiometers, output jacks, indicator lights, and meters are possible within a power supply unit depending upon the end result desired. This invention broadly relates to a basic laboratory power supply unit including an incoming line adapted to be connected to a source of electrical power, means to vary the voltage within the power supply unit, and output means for connecting suit able electrical apparatus to the power supply unit.

The apparatus of this invention comprises a monitoring control for opening and closing at least one side of the incoming line of the power supply unit. As shown more clearly in FIG. 3, the control of this invention comprises a key operated tumbler lock 38 mounted to the front panel 14. The tumbler lock includes a key plug 40 (FIG. I) rotatable in a lock cylinder 42 with a keyway 44 accessible from an exterior surface of the power supply unit. As is shown in FIG. 3, the external cylindrical surface of the lock cylinder 42 may be threaded as at 43 inorder to receive a pair of lock nuts 46, 46' to firmly clamp the tumbler lock 38 to the front panel 14. A bracket 48 is clamped to the internal wall of front panel 14 by means of the internal lock nut 46. Bracket 48 is generally U- shaped including a pair of legs having inturned edges 50 for the purpose of retaining a pair of circuit breaker elements 52, 54. Fasteners 57 are used to secure the circuit breaker elements to the inturned edges 50 of bracket 48.

Circuit breaker elements 52, 54 of FIG. 3 are multiterminal fully magnetic heavy duty industrial circuit breakers which serve as an on-off switch to open both the positive and negative sides of the incoming line of the power supply unit. Circuit breaker elements 52, 54 are identical and include internal switching means (not shown) adapted to open in the event of an overloaded condition of the incoming line and external reset arms 56, 58 respectively adapted to reset the internal switching means to a closed position. The circuit breaker elements 52, 54 of FIG. 3 are manufactured by Airpax Electronics, Inc. (Cambridge Division). For a more complete description of the operation of the circuit breaker elements 52, 54, reference is made to the Airpax Electronics, Inc. catalogue illustrating circuit breaker APL31-203-3. It is to be understood that the external reset arms 56, 58 are linked to the internal switching means of the respective circuit breaker elements 52, 54 such that after tripping of the internal switching means, the external reset arms 56, 58 may reset said internal switching means to a closed position. As is characteristic of the Airpax Electronics, Inc. circuit breaker described above, a lost motion connection is provided between the external reset arms 56, '58 and the internal switching means such that the internal switching means may open independently of the external reset arms 56, 58. Thus, in the event that the external reset arms 56, 58 are held in the on position of FIG. 3, the lost motion means within the circuit breaker elements permits the internal switching means to open independently of the external reset'arms. The advantage of this lost motion connection between the internal and external switching means will become more apparent as the description proceeds.

Interconnecting the key plug 40* of the tumbler lock 38 and the external reset arms 56, 58 is a linkage comprising a connecting arm -60 nonrotatably secured to the key plug 40 and a pin 62 disposed within passageways defined within the external reset arms 56, '58. A nut 64 and locking washer 66 may be disposed about a threaded end of the key plug 40' in order to firmly secure the connecting arm 60 thereto. It is thus to be understood that the connecting arm 60, nut 64 and lock washer 66 rotate with the key plug 40 disposed within lock cylinder 42. Rotation of the key plug 40 is accomplished as by inserting a suitable key within keyway 44 and thereafter rotating the key.

As shown in FIG. 3, the circuit breaker elements 52, 54 are disposed generally normal to the axis of the key plug 40 such that the pin 62 is generally normal to the connecting arm 60 with one end of pin 62 disposed within a passageway 69 of the connecting arm 60. Spacer elements 70 are disposed about pin 62. A pair of clips 72 are positioned on the pin 62 at either end thereof in order to hold the pin in place. As will be evident from FIG. 5, passageway 69 within the connecting arm 60 is considerably larger than the cross section of the pin 62 and spacer element 70 in order to insure that the connecting arm may freely rotate without binding the pin 62 or the spacer elements 70. The on-olf positions of the connecting arm 60' are shown in FIG. 5. It is thus to be understood that when the connecting arm 60' is moved from one position to the other, engagement of the walls defining passageway 69 of the connecting arm 60 and the spacer elements 70 disposed about pin 62 will produce simultaneous movement of the external reset arms 56, 58 to one or the other positions illustrated in FIGS. 3 and 4. The dual positions of the connecting arm 60 and the key 68 are illustrated in FIG. 2.

It is to be understood that the circuit breaker elements are inserted into the circuitry of the power supply unit as by connecting a respective terminal 73 (-FIG. 2) of each circuit breaker element to a respective side of the incoming line and by connecting a respective terminal 74 of each circuit breaker element to the load. A third terminal 76 may be provided for shunt operation of the circuit breaker. It is to be understood that the internal switching means of the circuit breaker elements serves to open the line between terminal 73 and terminals 74, 76. Whereas, as is shown in FIG. 3, a pair of circuit breaker elements are installed in the power supply unit to open each side of the incoming line to the power supply unit, it should be understood that this invention is equally applicable to a single circuit breaker element connected in series with one side of the incoming line.

With power supplied to the output jacks, the indicating light 36 will be on. In the event that the power supply unit is later short circuited (due for instance to improper student use of laboratory equipment) the circuit breaker elements 52, 54 will open thereby disconnecting all power from both sides of the incoming line. With power thus interrupted, the indicator light 36 will go out. It should be pointed out at this time that the circuit breaker elements 52, 54 in opening will do so because the internal switching means of the circuit breaker elements have opened independently of the external reset arms 56, 58. As is characteristic of standard tumbler locks, the plug 40 of the lock may not be rotated with the key removed. The lost motion connection between the internal switching means of the circuit breaker elements and the ex ternal reset arms permits the internal switching means to open in spite of the fact that the external reset arms are locked in place by the nonrotating connecting arm 60 (with the key 68 removed).

With the circuit breaker elements having opened due to an overloaded incoming line, the power supply unit is now completely safe. At this point, it is anticipated that the student will check his work to ascertain the nature of the overloaded condition of the incoming line. Since the student cannot reactivate the power supply unit himself, he must summon his instructor who, after inspecting the circuit, will insert the proper key in keyway 44 and turn the key plug 40 first to the off position (as shown in FIG. 1) and thereafter to the on position. The circuit breaker elements are thus reset and the student is prepared to continue with the experiment. Moreover, the laboratory instructor has been given an opportunity to inspect the students work after an overloaded condition. The possibility of damaging costly electronic equipment through misuse of the circuit breaker has been completely eliminated by the control apparatus of this invention.

It is contemplated that advanced laboratory students may be permitted to retain a key to their power supply unit since they will be permitted to reactivate the unit themselves in the event of inadvertent overloading of the circuit. Key operation of the circuit breaker also prevents access to the power supply unit by unauthorized personnel. With the circuit breaker in the open or oil position and the key removed, the student may be assured that his work will not be disturbed by unauthorized personnel.

METHOD OF SENSING AND CORRECTING AN OVERLOADED CIRCUIT This invention is also directed to a method of sensing and correcting an overloaded circuit including a power supply unit with an incoming line adapted to be connected to a source of electrical power, means within the power supply unit to vary the voltage, and output means for connecting electrical apparatus to the power supply unit. The method steps of this invention include the steps of:

(a) Providing a key operated tumbler lock including a key plug rotatable in a lock cylinder with a keyway accessible from the exterior of the power supply unit.

(b) Providing a mechanical linkage between the key plug and an external reset arm of a circuit breaker connected in series with at least one side of the incoming line of the power supply unit, the circuit breaker having internal switching means adapted to open in the event of an overloaded condition of the incoming line.

(0) Providing a lost motion linkage between the internal switching means of the circuit breaker and the key plug permitting the internal switching means of the circuit breaker to open independently of the key plug.

(d) Connecting electrical apparatus to the power supply unit output means.

(e) Sensing an open internal switching means condition in the circuit breaker.

(f) Correcting the circuit condition which created the open internal switching means condition.

(g) Inserting a key adapted to be received in said keyway and turning said key plug to thereby turn the external reset arm and thus reset the internal switching means of the circuit breaker.

(h) Removing the key from the keyway.

MODIFICATIONS AND EXTENSION OF THE INVENTION While this invention has been described with reference to a power supply unit for use in a laboratory, the apparatus and method of this invention should not be considered as limited to student use in a laboratory since the invention is broadly applicable to many uses of a circuit breaker. Tumbler lock resetting of the circuit breaker prevents access to the circuit breaker by unauthorized personnel. For security reasons in industry it may be necessary for a watchman or guard to inspect and reset the circuit breaker with his key after an overloaded condition has been noted in the circuit. This invention, therefore, has broad application as a security means for limiting access to the circuit breaker of a circuit.

While this invention has been described with particular reference to a circuit breaker of Airpax Electronics, Inc. (Cambridge division), other circuit breakers of the same general type can be used in conjunction with a tumbler lock within the spirit of this invention. The circuit breaker described is particularly well suited to this invention as it may be readily mounted to the support bracket 48 and fastened to the front panel 14 of the power supply unit. In addition, the circuit breaker described is particularly well suited to this invention as it includes an internal lost motion tripping feature. This permits the internal switching means to open even with the external reset arm held in the on position as removal of the key from the keyway serves to lock the external reset arm in the on position. The lost motion connection between the internal switching means and the external reset arm permits the internal switching means to open in the event of an overloaded condition of the circuit without requiring movement of the external reset arm or the key plug. Other circuit breakers of this general type can be used with this invention.

Within the scope of this invention should be considered other structures permitting a lost motion connection between the internal switching means of the circuit breaker and the key plug. In the preferred embodiment of this invention, the lost motion linkage between the key plug and the internal switching means is located within the circuit breaker between the external reset arm and the internal switching means. As a logical extension of this invention should be considered structures wherein the key plug of the tumbler lock is capable of rotating in one direction with the key removed. Thus, whereas the key may be required to turn the key plug from the oil to the on position, special tumbler locks are available wherein the key plug could be rotated from the on to the off position with the key removed. With such a tumbler lock it would be possible to utilize a circuit breaker wherein there is a direct linkage between the internal switching means, the external reset arm, and the key plug. Upon reaching an overloaded condition, the entire circuit breaker including the internal switching means, the external reset arm, and the linkage interconnecting the circuit breaker and the key plug would switch to the open or 01f position.

Alternately, as a logical extension of this invention, it is possible to provide a lost motion connection between the connecting arm 60 of the key plug 40 and pin 62 of the external reset arms, 56, 58. Thus, by providing an elongated slot within the connecting arm 60 (in lieu of passageway 69, FIG. 5) it is possible to permit the external reset arms of the circuit breaker elements to trip to the open position with the connecting arm held stationary by a nonrotating key plug 40. The elongated slot in the connecting arm 60 would accommodate movement of the pin 62 and spacer elements 70 therein, thus providing a lost motion connection between the internal switching means of the circuit breaker and the key plug.

The above examples are cited to demonstrate the variety of lost motion linkage means that may be utilized within the scope and spirit of this invention.

The indicator light 36 of the front panel 14 has been described as normally illuminated to indicate power at the various outlets at the power supply unit. Within the scope of the method of this invention should be considered other structures for sensing the opening of the internal switching means of the circuit breaker elements such as an audio alarm, a meter, or other signaling devices well known to those skilled in the art.

For ease of description, the principles of this invention have been set forth in connection with but a single illustrated embodiment showing the apparatus of this invention. The illustrated embodiment and the terminology employed in describing it are not to be considered as limiting inasmuch as variations in these may be made without departing from the spirit of this invention. It is desired that the apparatus and method of this invention be restricted only by the scope of the appended claims.

The invention claimed is:

1. In an electrical power supply unit comprising an incoming line having a positive and negative side adapted to be connected to a source of electrical power, means to vary the voltage, and output means for connecting electrical apparatus to the power supply unit; a monitoring 8 control for opening and closing at least one side of the incoming line, said control comprising:

a key operated tumbler lock including a key plug rotatable in a lock cylinder with a keyway accessible from an exterior surface of the power supply unit;

a key adapted to be received in said keyway to turn said key plug;

a circuit breaker connected in series with at least one side of said incoming line and having internal switching means adapted to open in the event of an overloaded condition of said incoming line and further including an external reset arm adapted to reset said internal switching means to a closed position;

linkage means interconnecting said key plug and said external reset arm whereby said internal switching means may be reset by said key;

lost motion means to permit said internal switching means to open independently of said key plug.

2. The invention of claim 1 in which said lost motion means is defined as a lost motion connection between said internal switching means and said external reset arm.

3. The invention of claim 1 in which said linkage means is defined as a radial connecting arm secured to said key plug and a pin secured to said external reset arm with a connecting means between said connecting arm and said pin.

4. The invention of claim 3 in which said connecting means is defined as a slot in said connecting arm with an end of said pin disposed within said slot.

5. A method of protecting against damage to electrical equipment caused by an overloaded circuit which circuit includes an electrical power supply unit which includes an incoming line having a positive and negative side adapted to be connected to a source of electrical power, means to vary the voltage, output means for connecting electrical apparatus to the power supply unit, a circuit breaker connected in series with at least one side of the incoming line and having internal switching means adapted to open in the event of an overloaded condition of the incoming line and further including an external reset arm adapted to reset the internal switching means to a closed position, a key operated tumbler lock including a key plug rotatable in a lock cylinder with a keyway accessible from the exterior of the power supply unit, a mechanical linkage between the key plug and the external reset arm, a lost motion linkage between the internal switching means and the key plug permitting the internal switching means to open independently of the key plug, and an electrical apparatus connected to the power supply 50 unit output means, comprising the steps of:

(a) sensing an open internal switching means condition in the circuit breaker;

(b) correcting the circuit condition which created said open internal switching means condition;

(c) inserting a key adapted to be received in said keyway and turning said key plug to reset said internal switching means;

(d) removing said key from said keyway.

References Cited 

